COUPLING CONSTANT, DOUBLE RESONANCE AND APPLICATION OF NMR & MCQ

COUPLING CONSTANT, DOUBLE RESONANCE AND APPLICATION OF NMR & MCQ

COUPLING CONSTANT :-

Defination:- The distance between the center of the two peak in NMR spect is known as the COUPLING CONSTANT.

It is used to differentiate two singlet, one doublet, one quartertet etc.

It is denoted by “J”.

Unit of J is Hz, cycle per second.

Coupling constant value is constant and it is positive or negative.

Coupling constant value depends on mainly two factor

  • 1. No. Of covalent bond
  • 2. Structure realtion ship between two coupled proton.

Coupling constant are mainly two types

1. Geminal constant :– proton that attached with same carbon but environment is different is known as geminal proton and distance between two peak of this proton are called Geminal constant.

Value of Geminal constant is increase with electronegative of atom.

Value is also increase with bond angle.

2. Vicinal coupling :– vicinal proton are proton which are reparated by three bond.

3. Longer range coupling :- No coupling observed for distance between two observed nuclei is more than 3 covalent bond. But unsaturated/ fluorocompound

Show appreciate coupling for the distance of more than 3 co valent bond in higher solution spectrometer.

DOUBLE RESONANCE

This is a technique which involves irradiation of proton or set of proton this irradiated is done by intense radio frequency energy. This energy is eliminated spin spin coupling amongst proton.

Application of NMR

1. Structure elucidation of organic compound.

2. Investigation of dynamic property of molecules ex. Hydrogen bond, keto-enol tautomerism.

3. Determine of optical purity.

4. Study of molecular interaction like micelle formation.

5. Quantitative analysis

a. Assay of components

b. Hydrogen analysis

C. Iodine value

D. moisture analysis

MCQ

1. Which technique are used to determine iodine value ?

A. IR

B. NMR

C. UV

D. Mass spectroscopy

Ans. B

2. Which technique is used to determine mositure in percentage ?

A. Karl Fischer titration

B. NMR

C. A and B

D. None of this

Ans. C

3. Which is unit of coupling constant?

A. Hz

B. CPS

C. A and B

D. None of this

Ans c

4. If bond angle is decrease then value of Geminal constant is

A. Increase

B. Decrease

C. Constant

D. All of the

Ans.B

5. If coupling constant value is positive, what it suggests ?

A. Two nuclei are same direction

B. Two nuclei are opposite direction

C. A and B

D. None of this

Ans. B

6. If the nuclei have same direction value of coupling constant is ?

A. Negative

B. Positive

C. Zero

D. 1

Ans. A

7. Which technique are is used for structure elucidation?

A. NMR

B . Diazotization

C. Kjeldahl Titration

D . RIA

Ans A

8. Which technique is used to study micelle formation ?

A. NMR

B. IR

C. UV

D. Atomic absorption

Ans. A

9. Which technique is used to study keto enol tautomerism ?

A. NMR

B. UV

C. IR

D. All of the

Ans.A

10. Hydrogen bonding is property is investigation by which method ?

A. Nmr

B. IR

C. uv

D. None of this

Ans A

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Reference: Text book of Pharmaceutical Analysis third edition by Dr. S. Ravi Sankar -Page no. 6.8 to 6.19

text book of Pharmaceutical Analysis by Y R Sharma Page no 203 to 208

 

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